Certain data communication networks, such as those based on the well-known synchronous optical network (SONET) or synchronous digital hierarchy (SDH) standards, can be configured to utilize a technique known as virtual concatenation. The SONET standard is described in Bellcore standards document GR-253 and ANSI standards document T1.105, both of which are incorporated by reference herein. Virtual concatenation in the SONET context is defined in greater detail in the ANSI T1.105-199x standards document, which is part of the above-cited T1.105 document. The SDH standard is described in ITU-T standards document G.707, which is incorporated by reference herein.
Additional details regarding conventional aspects of virtual concatenation can be found in, for example, D. Cavendish et al., “New Transport Services for Next-Generation SONET/SDH Systems,” IEEE Communications Magazine, pp. 80-97, May 2002, which is incorporated by reference herein.
In general, virtual concatenation allows a given data communication channel, also referred to as a virtual concatenation (VC) data stream, to be split into several smaller streams, commonly referred to as VC member streams. The set of VC member streams associated with a given VC data stream is also referred to as a virtually concatenated group (VCG) or a VC group. Each of the VC member streams can travel along a different path from a source node to a destination node. As a result, the different member streams typically experience different delays in transit from the source node to the destination node. Upon arrival at the destination node, the individual member streams are recombined into the original VC stream. This splitting and recombining of data traffic is designed to be completely invisible to the transmitting or receiving end users, and allows for a particularly efficient utilization of network bandwidth.
However, this bandwidth efficiency is obtained at the price of increased algorithmic complexity. In particular, the recombining of the individual VC member streams at the destination node requires special care. For example, the destination node must account for the fact that these individual member streams are likely to have encountered different delays along their respective paths. Furthermore, these delays may not be fixed, due to slight variations in the SONET clocks in the various paths. A process known as differential delay compensation is used to realign the individual member streams.
The complexity of the differential delay compensation process is significantly increased if a given VC system is configured to support a protocol known as link capacity adjustment scheme (LCAS). Such a system is referred to herein as a VC/LCAS system. The LCAS protocol allows the system to dynamically add a member stream to, or subtract a member stream from, an existing VC group. This addition or subtraction of a member stream results in a respective increase or decrease in overall data throughput or bandwidth.
The LCAS protocol generally requires that the bandwidth adjustment be configured so as not to introduce errors or otherwise alter the data stream, a requirement also referred to as “hitless” addition and subtraction of bandwidth. Therefore, in a VC/LCAS system, the differential delay compensation process must be capable of accommodating this dynamic change in the individual member delays with respect to the overall group.
Once the destination node has re-aligned the individual member streams utilizing the delay compensation process, it can, for example, process the data and thereby terminate the data path, or re-package the data into an aligned VC/LCAS stream and send it to a downstream network component for further processing. In the latter case, where the data is sent out as VC/LCAS stream, problems can arise in the conventional delay compensation process, particularly with the addition of a new member to an existing group.
It is therefore apparent that a need exists for improved delay compensation in virtual concatenation applications, and more specifically for delay compensation techniques capable of providing efficient support for hitless addition or subtraction of bandwidth in accordance with LCAS or other similar protocol.